In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, which may also be referred to as a beam or a beam group, with each service area or cell area being served by a radio network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a NodeB, eNodeB (eNB), or gNB as denoted in 5G. A service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio network node.
Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network also referred to as 5G New Radio (NR). The EPS comprises the Evolved Universal Terrestrial Radio Access Network (EUTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs used in 3G networks. In general, in E-UTRAN/LTE the functions of a 3G RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface.
Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a Multiple-Input Multiple-Output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO.
In addition to faster peak Internet connection speeds, 5G planning aims at higher capacity than current 4G, allowing higher number of mobile broadband users per area unit, and allowing consumption of higher or unlimited data quantities in gigabyte per month and user. This would make it feasible for a large portion of the population to stream high-definition media many hours per day with their mobile devices, when out of reach of Wi-Fi hotspots. 5G research and development also aims at improved support of machine to machine communication, also known as the Internet of things, aiming at lower cost, lower battery consumption and lower latency than 4G equipment.
5G currently being studied by 3GPP is targeting a wide range of data services including Enhanced Mobile Broadband (eMBB) and Ultra-Reliable Low Latency Communication (URLLC). URLLC is a new data service with extremely strict error and latency requirements. URLLC will enhance the way of communication with extremely challenging requirements including 1 ms end-to-end radio link latency and guaranteed minimum reliability of 99.999%.
Some of the use cases for URLLC may be robotics, industrial automation, remote surgery and health care, interactive augmented-virtual reality, smart vehicles, transport and infrastructure, drones and aircraft communication, etc.
To enable optimization for different services, the length of the Transmission Time interval (TTI) is expected to vary. For instance, URLLC may have a shorter TTI length than eMBB. URLLC data transmission is supposed to happen as soon as URLLC packet arrives at the transmitter, while at the same time the eMBB transmission may be transmitted or be scheduled to be transmitted. It is therefore desirable to puncture, also referred as interrupt, the eMBB transmission in certain time-frequency resources and perform a ULLRC transmission on those punctured resources.
NR supports slot-based transmissions such as Physical Downlink Shared Channel (PDSCH) and Physical Uplink Shared Channel (PUSCH) Type A and mini-slots and non-slot-based transmissions such as PDSCH and PUSCH Type B.
In the following, the wording mini-slot may refer to PDSCH and/or PUSCH type B. For mini-slot, the transmission may start at any symbol, Demodulation Reference Signals (DMRS) are relative to the transmission start and the length may e.g. be from 1 to 13 symbols. Although the standard has not specifically stated, it is a common practice that URLLC data may utilize mini-slot transmission. On the other hand, slot-based transmission may have 14 OFDM symbols.
In the following, it is implicitly assume that URLLC data uses mini-slot transmission, while eMBB data uses slot transmission.
It has been agreed that for DL in 3GPP, dynamic resource sharing between URLLC and eMBB is supported by transmitting URLLC scheduled traffic, and in particular URLLC transmission on mini-slot transmission may occur in resources scheduled for ongoing eMBB traffic on slot transmission.
In uplink (UL) i.e. from the UE to the gNB, the UE transmits eMBB data, which is punctured by URLLC data transmitted in the resources scheduled for eMBB, as illustrated in FIG. 1. FIG. 1 is an illustration of a URLLC transmission puncturing eMBB data in uplink.
In Downlink (DL) i.e. from the gNB to the UE, the URLLC transmission comprises a control information part comprising De-modulation Reference Signals (DMRS) for demodulation of the control information as well as control information, and a data part comprising DMRS for demodulation of data as well as data. FIG. 2 illustrates a scenario where the eMBB data transmission is punctured by URLLC data in downlink. FIG. 2 is an illustration of a URLLC transmission puncturing eMBB data in downlink.
The reliability of the punctured data will be provided by performing Hybrid Automatic Repeat Request (HARQ) re-transmissions when it is necessary. In many wireless communications systems, HARQ re-transmissions are a method to handle un-predicable interference and channel variations.
The LTE HARQ mechanism, however, comprises multiple stop-and-wait protocols that may be applied in parallel to allow continuous transmission of data. In LTE, for either DL or UL, there is one HARQ entity per serving cell. HARQ processes may belong to the same HARQ entity, but have independent HARQ acknowledgements. Transmission Time interval (TTI) is a parameter in LTE related to encapsulation of data from higher layers into sub frames for transmission on the radio link layer. The TTI such as the subframe has 1 ms duration and the HARQ-Acknowledgement (ACK), for Frequency Division Duplex (FDD), is transmitted in subframe n+4 for a data transmission in subframe n. In LTE uplink, the HARQ retransmission timing is fixed, and the HARQ retransmission process typically takes 8 ms for each retransmission. When a receiver has attempted to decode a data message, it transmits an indicator to the transmitter indicating whether the decoding was successful or not. When the transmitter receives an indicator indicating un-successful decoding the transmitter typically performs a re-transmission of the data message which the receiver most likely will soft-combine with the original received transmission.
The fixed HARQ feedback timing is a problem in some implementation scenarios, e.g. with centralized baseband deployment or non-ideal backhaul, and when operating in unlicensed spectrum, e.g. where listen-before-talk sometimes prevents UEs from sending HARQ feedback. 5G shall have a lean and scalable design to be able to cope with various latencies on the transport and radio interface as well as with different processing capabilities on UE and network side.
A NACK referred in the following may be in a DCI-like one to contain one or more of the following info: MCS, redundancy version (RV), NDI, etc as well as any possible indication of physical resource allocation (change).
The HARQ-ACK response send by a network node may e.g. be of either format:
(a) PHICH-like. The DL response to a UL TB tansmission carries only ACK/NACK information, and does not carry full scheduling information like MCS, resource allocation, etc. The advantage of the PHICH-like response is that it has 1-bit payload only, hence very easy to transmit reliably over the air to UE. The disadvantage is that a new physical channel, or a new DCI format, has to be introduced to provide such feedback in NR.
(b) PDCCH-like. As discussed above, the DL response to a UL TB transmission can contain scheduling information rather than simple ACK/NACK information. The advantage is that it can reuse DCI format defined for other traffic (e.g., eMBB) for URLLC traffic as well. The disadvantage is that the DCI payload is much larger, typically in the range of 20-80 bits. The larger payload leads to lower reliability.
To facilitate latency reduction for URLLC traffic, mini-slot-based transmissions of 2 or a few of OFDM symbols are configured. On the other hand, eMBB traffic uses slot transmission with more OFDM symbols such as 7, or longer. URLLC UEs are allocated dedicated Scheduling Request (SR), here called URLLC-SR, resources with a mini-slot periodicity. Note that SRs requires fewer resources than data transmissions as in Semi-Persistent Scheduling (SPS) framework. In addition, the HARQ feedback is sent at a Physical Downlink Control Channel (PDCCH). There are two types of PDCCH: Slot-PDCCH and mini-slot-PDCCH. Mini-slot-PDCCH repeats every mini-slot and can provide fast feedback.
E.g., see Ericsson white paper Uen 284 23-3204 Rev C April 2016.